Iron-deficiency anemia (IDA) during early development has brain and behavior effects that may have lifelong consequences. Animal models show long-lasting changes in brain architecture, function and associated behaviors. IDA in infants is associated with poorer motor, cognitive, social-emotional, and neurophysiologic outcomes during iron deficiency and years later. The proposed project will determine long-term neurobiological effects of IDA in infancy (Aim 1), adult functional outcomes related to preventing IDA in infancy (Aim 2), and long-term effects of giving iron to iron-sufficient infants (Aim 3). Itis the only large, longitudinal study of IDA and its prevention in healthy full-term infants. Over 110 Chileans, who will be 21 years old, participated in preventive trial and/or neurobiology aspects of an iron deficiency project as infants, with follow up at 4-5, 10, and 16 y. In addition, the cohrt has had assessment of functional genetic polymorphisms related to iron regulation, neurotransmitter function, and behavior. For Aim 1, we will continue state-of-art neurophysiologic, neuroimaging (ERP), and behavioral testing for hypotheses regarding long-lasting effects of early IDA on neurocognitive and regulatory functions (sleep-wake cycle, neuroendocrine) and their integration into complex behaviors. These sophisticated neurobiological studies will be conducted in a subset of the larger cohort, 90 21-year-olds with infancy IDA and 65 non-anemic controls. We predict that disruption in sleep-wake cycle in the former IDA group will disturb systems related to cognition and emotion. Longitudinal analysis will determine which effects are transient, persistent, or emergent through young adulthood. We hypothesize that participants with early IDA and vulnerable genotypes will show more adverse outcomes as young adults. Aim 2 pursues our observations of more adaptive behavior in infancy and 10 y among participants randomized to prophylactic iron in infancy. At 21 y, we predict that infancy iron supplementation will contribute to better functional outcomes, including educational trajectories, job potential, mental health, and close relationships (n ~ 1028). We expect genetic interactions-iron will be more beneficial for individuals with genotypes associated with increased risk for iron deficiency and/or poorer mental health or cognitive function. Aim 3 addresses universal iron supplementation in infancy and potential risks in giving iron to iron-sufficient infants. We will compare adulthood functioning in 258 individuals randomized to high-iron formula in infancy and 230 randomized to low- iron formula. We will also compare our very sensitive neurobiological outcomes in 33 participants who were iron-sufficient in infancy and treated with medicinal iron for at least 6 mo and 33 who were untreated. This study remains at the forefront of determining long-term brain and behavioral effects of IDA, its prevention in the healthy full-term human infant, and potential risks of providing iron to iron-sufficient infants.